Abdul Waheed

The application of direct membrane filtration can reduce the space and energy footprint of the treatment process.

This study focuses on tuning active‐layer features by altering the chemistry of the underlying polyacrylonitrile (PAN) to assess its impact on the membranes' organic‐solvent nanofiltration (OSN). The PAN supports are tailored via diamine crosslinking (1,3‐diaminopropane (DAP), ethylene diamine [EDA], and hydrazine [Hz]) and hydrolysis, and the resulting supports were used for interfacial polymerization (IP) to develop a poly(piperazine amide) active layer. Use of hydrolyzed and EDA crosslinked supports leads to hydrophilic surface wettability, with water contact angles (WCAs) of 35.4° and 33.93°, respectively. The separation efficiencies of the membranes have also been tested using various dyes in different solvent media. In terms of separation performance, the EDA cross‐linked thin‐film composite (TFC) membrane shows a balanced behavior in terms of selectivity‐permeability trade‐off, whereas the Hz cross‐linked TFC membrane (PAN support crosslinked using hydrazine) has an organophilic feature, and the hydrolyzed TFC membrane is the most hydrophilic with a water permeance of 18.3 L m ⁻² h ⁻¹ bar ⁻¹ . In the case of rejection of solutes with varying molecular sizes and charges, the EDA cross‐linked TFC membrane shows improved performance in methanol and ethanol, whereas Hz and hydrolyzed supported TFC membranes show reduced selectivity for the model cationic Methylene Blue (MB) dye.

Millions of End-of-Life (EoL) reverse osmosis (RO) membranes are discarded each year by desalination facilities worldwide. This poses a significant environmental challenge, as large amounts of solid waste are often managed through landfilling or incineration. Recycling EoL RO membranes for reuse as nanofiltration (NF) or ultrafiltration (UF) membranes is an attractive pathway for the effective management of solid waste. However, the commonly adopted route to degrade the polyamide active layer of the EoL membranes for recycling and reuse requires high-intensity exposure of the membranes to the NaOCl solution. There is a need to develop a route to make membranes more responsive to the low dosage of NaOCl for recycling and reuse of the membranes. The current study explored that tailoring of the membrane active layer could generate a more responsive polyamide membrane to a mild concentration of NaOCl. This was achieved by incorporating monobenzoyl chlorinated aromatic reactants 4-nitrobenzoyl chloride (4-NC) and 3,5-dinitrobenzoyl chloride (3,5-DNC) into the active layer of the membranes. A minor concentration of the 4-NC and 3,5-DNC was added to the trimesoyl chloride-containing organic phase during interfacial polymerization with m-phenylenediamine. Owing to the presence of only one reactive site in 4-NC and 3,5-DNC, the reaction with m-phenylenediamine can hinder crosslinking in certain regions of the m-phenylenediamine and trimesoyl chloride polyamide active layer. This limited number of uncross-linked regions not only increases the membrane permeability with reasonable salt rejection but also makes the membranes more responsive to chlorine. This was realized when the permeate flux was found to be 108, 114, and 200 L m⁻² h⁻¹ for the M1 (control), M2 (4-NC), and M3 (3,5-DNC) membranes, respectively, at a feed pressure of 30 bar using 100 ppm of NaOCl for 24 h. On the other hand, the rejection of NaCl was decreased from 97 to 9.6, 93 to 7.1, and 91 to 3.6% with an increase in contact time from 2 h to 24 h for M1, M2, and M3 membranes, respectively. This exposure intensity was significantly less than that commonly used in the literature. Furthermore, the recycled modified membrane, especially M3, showed reversible fouling when the membranes were tested using bovine serum albumin as a model foulant in seawater scenarios.

With an emerging trend of using ultrafiltration (UF) membranes for advanced seawater pretreatment, the current study aims to enhance the chemical and pH stability of polyacrylonitrile (PAN)‐based UF membranes for seawater pretreatment applications. This was achieved using a simple and facile approach of crosslinking the PAN membranes with diamines of varying lengths of carbon chains. Diamines include hydrazine (Hz), ethylene diamine (EDA), and diamino propane (DAP), which were used to crosslink nitrile (‐C≡N) groups on the PAN chains giving rise to imine linkages. In addition, a hydrolyzed (Hy) PAN membrane and a control neat PAN membrane were also prepared. Developed membranes showed excellent pretreatment potential for open seawater intake. Among the different membranes, the EDA‐PAN membrane was superior, especially in terms of lower fouling tendency compared to other membranes. The EDA‐PAN membrane showed rejections of > 95% and > 99% in the case of algal biomass and oil–water emulsion, respectively. EDA‐PAN membrane showed resistance to membrane fouling with R_F values of 3.00 × 10¹⁰ and 1.24 × 10¹¹ m⁻¹ for humic acid and bovine serum albumin, respectively. More importantly, crosslinked membranes such as EDA‐PAN showed increased stability toward corrosive polar solvents like N‐methyl pyrrolidone (NMP), and acid–base exposures compared to the control membrane.

The potential of polymeric amines in fabricating organic solvent nanofiltration (OSN) membranes has largely been unexplored. In this study, we employed polyvinyl amine (PVAm) as an aqueous monomer, cross‐linked with trimesoyl chloride (TMC) as an organic phase monomer, to fabricate a polyamide (PA) active layer on polyacrylonitrile (PAN) support. A set of nine membranes was prepared for optimizing the membrane structure by varying the PVAm concentration and duration of IP. It was found that increasing the PVAm concentration or IP duration resulted in increasing the rejection and lowering the permeance of the membranes. This was due to decreasing molecular weight cutoffs (MWCOs) of the membranes. Among different membranes, M2a was found to be best optimized with an MWCO of around 350 Da and demonstrated superior rejection capabilities, exceeding 99% for congo red (CR) and eriochrome black T (EBT), while 93% and 90% for methyl orange (MO) and methylene blue (MB), respectively. Among the polar solvents, methanol achieved the highest permeance of 3.8 L m⁻² h⁻¹ bar⁻¹, while n‐hexane, a nonpolar solvent, showed a permeance of 4.2 L m⁻² h⁻¹ bar⁻¹. This study highlights the potential of polymeric amines, varying their concentrations and duration of IP in developing efficient OSN membranes.

The scarcity of freshwater resources, driven by rapid population growth and industrialization, underscores the urgent need for advanced desalination technologies. This research aims to meet this critical demand by enhancing the performance of polyamide membranes through innovative chemical tuning of the active layer. By strategically using Boc-protected ethylenediamine (EDA), we can precisely control the membrane’s surface properties. One amino group in EDA is protected with a Boc group, allowing the other to participate in the interfacial polymerization (IP) reaction with meta-phenylenediamine (MPD) and trimesoyl chloride (TMC). This inclusion of Boc-protected EDA enables in situ tuning of the active layer chemistry during polymerization. Subsequent removal of the Boc protection generates hydrophilic ammonium groups on the membrane surface, enhancing its desalination capabilities. As a result, three distinct membranes were fabricated and thoroughly characterized: MPD-TMC (control), MPD-TMC-EDA-Boc, and MPD-TMC-EDA-Deboc. At 20 bar and 2000 ppm NaCl feed, the MPD-TMC-EDA-Deboc membrane demonstrated superior desalination performance with a salt rejection of 98 ± 0.5% and a permeate flux of 25 L m⁻² h⁻¹; an increase of 25% compared to the control membrane. For the seawater nanofiltration (NF) permeate with a TDS of 33,700 ppm, a salt rejection of 97% and a permeate flux of 23 L m⁻² h⁻¹ was recorded at 20 bar. The MPD-TMC-EDA-Deboc membrane showed enhanced antifouling performance (95 ± 1% flux recovery) compared to the control MPD-TMC membrane with 93 ± 1% flux recovery. The Boc-protection/deprotection strategy demonstrated the high potential of this approach to significantly enhance the performance of polyamide membranes for desalination applications.

Treating oily wastewater streams such as produced water has a huge potential to resolve the issue of wastewater disposal and generate useful water for reuse. Among different techniques employed for oily wastewater (oil-in-water; O/W emulsion) treatment, membrane-based separation is advantageous owing to its lower energy consumption, recycling, ease of operation, and wider scope of tuning the active layer chemistry for enhanced performance. In line with the possibilities of enhancing the performance of the membranes for efficient O/W emulsion separation, the current work is designed to yield five different variants of polyaniline (PANI) active layers with special surface wettability features (superhyrophilic and underwater superoleophobic) on a ceramic alumina support. To achieve variants of PANI on ceramic alumina supports, emulsion polymerization was carried out, and different concentrations of initiator ammonium persulfate (APS) were applied to lead to PANI-A@Aluminum Oxide membrane, PANI-B@Aluminum Oxide membrane, PANI-C@Aluminum Oxide membrane, PANI-D@Aluminum Oxide membrane, and PANI-E@Aluminum Oxide membrane corresponding to 0.15, 0.25, 0.35, 0.5, and 1.0 M concentrations of initiator. The variation in initiator concentration resulted in different PANI growth patterns; hence, the resultant membranes showed different structural, physical, and performance features. Different characterization techniques including ¹H NMR, SEM, FE-TEM, AFM, water contact angle, XRD, EDX, and ATR-FTIR confirmed a more uniform and continuous growth of PANI (PANI-B) using a 0.25 M initiator concentration. The resultant PANI-B@Aluminum Oxide membrane showed an excellent surfactant stabilized crude O/W emulsion separation reaching >99% with a permeate flux of 2154 L m^-2 h^-1 (LMH) at 4 bar using a 100 ppm surfactant stabilized crude oil-in-water emulsion. The fouling and cleaning cycles revealed that the membrane can be reused with a 70% recovery of the initial permeate flux.